Yemenis in the southwestern city of Dhamar have taken to the streets in condemnation of a recent airstrike by the military coalition led by the regime in Riyadh that killed dozens of schoolchildren in northern Yemen.

Carrying placards and banners, the protesters on Saturday chanted slogans against Saudi Arabia and its allies.

On Thursday, the coalition warplanes attacked a school bus in a market in the town of Dahyan in Yemen’s northwestern province of Sa’ada. At least 50 civilians, mainly school kids, were killed and nearly 80 others were injured.

A few hours after the deadly strike, UN Secretary General António Guterres denounced the act of aggression and called for an independent investigation into the incident.

According to Yemen’s al-Masirah television network, the bus was transporting a group of young schoolchildren attending summer classes of the Holy Qur’an.

Johannes Bruwer, the head of the International Committee of the Red Cross (ICRC) delegation to Yemen, said in a posting on Twitter that most of those killed by the airstrike were children younger than 10 years of age.

The Saudi-led coalition, in a defiant statement, has described the massacre as a “legitimate action” to target missile launchers used by Yemen’s Houthi Ansarullah fighters to target the southern Saudi city of Jizan. Coalition spokesman Turki al-Malki even claimed that the strike “conformed to international and humanitarian laws.”

The Al Saud regime along with some of its allies, particularly the United Arab Emirates, has been engaged in a deadly war against impoverished Yemen since March 2015 in an attempt to reinstall former President Abd Rabbuh Mansur Hadi and crush the popular Ansarullah movement.